Sulfates--Physiological effect

Sulfide accumulation in carbonate sediments of tropical seagrass communities may be responsible for widespread die-back of Thalassia testudinum in Florida Bay. Root hydroponic chambers were used to determine the effects of below-ground exposure to 0.0, 2.0, 4.0, 6.0, and 10.0 mM sulfides. T. testudinum ATP, energy charge, photosynthesis and growth responses were determined after 48 h under light saturation. Root ATP, energy charge and adenylate ratios were all significantly reduced (P < 0.05) when exposed to 2.0-10.0 mM sulfides. Leaf elongation rates declined by an average of 43% in the 2.0-6.0 mM treatments and 63% in the 10.0 mM treatment. Although root energy charge, ATP production and leaf elongation rates declined after sulfide exposure, concentrations up to 10.0 mM failed to produce visual signs of sulfide toxicity or mortality. Photosynthesis and leaf EC remained high after sulfide treatments, suggesting a resilience of T. testudinum to short-term sulfide exposure.

Currently, there is a great deal of interest in the role of sulfur in the seagrass ecosystems and for sulfide, a known phytotoxin, in particular. This research used a 35S tracer technique to examine sulfur metabolism in the seagrass Thalassia testudinum. The uptake of the 35S radiotracer was documented at similar rates under both oxic and anoxic treatments. The highest total radioactivity was in root and rhizome tissue, as compared to the leaves. 35S translocation from roots to leaves was found to be more efficient in young versus mature leaves. Total sulfur uptake was estimated and found to be significantly different between root and rhizome tissue under oxic conditions. In the anoxic treatment, 1 mM sulfide may have been a threshold, at which the seagrass showed reduced uptake of 35S into the below-ground tissue. While the plants assisted in the production of sulfide in this experiment, sulfide accumulation may inhibit 35S uptake. This is counter to the idea of increased sulfide intrusion under sediment hypoxia. This study represents the first attempt to use 35S to trace sulfur incorporation into seagrass; further research will be required to understand the complex sulfur biochemistry of these important marine plants using this method.